A ball grid array (BGA) includes an array of balls of solder that are affixed to pins on the bottom of an integrated circuit (IC) package for electrically connecting the IC package to a printed circuit board (PCB). The IC package may then be placed on the PCB, which has copper conductive pads in a pattern that matches the array of solder balls on the IC package. The solder balls may be heated to cause the solder balls to melt. When the solder cools and solidifies, the hardened solder mechanically attaches the IC package to the PCB.
As shown in FIGS. 1A and 1B, a conventional BGA footprint on a PCB 100 includes a “dog-bone” footprint element 110. Dog-bone footprint element 110 typically includes a via 130, that provides a connecting hole through one or more layers of PCB 100, and a BGA pad 140 upon which a ball of solder of the BGA may be affixed via heating of the solder. A single dog-bone footprint element 110 is typically reproduced in columns 120 on PCB 100 such that the configuration of BGA pads 140 on PCB 100 matches the configuration of the BGA array. At 39.37 mil pitch, the configuration of the dog-bone footprint pattern on PCB 100 provides two routing channels 150 per PCB layer for each pair of columns 120 of the BGA (where a “routing channel” includes an area in the PCB where one conductive trace may be placed). Two routing channels 150 per PCB layer for two columns 120 of the BGA inhibits the “escape” of wiring for edge coupled differential pairs (i.e., pairs of conductors used for differential signaling), typically requiring the wiring for the differential pairs to be routed around vias. Such routing has a negative impact on the signal integrity associated with the differential pairs.
As shown in more detail in FIG. 1B, an existing dog-bone footprint element 110 may be arranged in columns 120, with vias 130 having a distance of d 180 between each successive via 130 in a vertical direction, and a same distance d 190 between each successive via 130 in a horizontal direction. Each dog-bone footprint element 110 may be formed on the PCB at an angle 160 of 45 degrees.